190 Journal of Agricultural Research voi.xx,No. 3 



greater or lesser amounts of them, despite the deficiency of chlorophyl 

 in the leaves; but the reasons why excessive amounts of these elements 

 accumulate in mottled citrus leaves are not clear. It seems probable 

 that some physico-chemical principle not elucidated by the preceding 

 data must be fundamentally involved. 



Before any explanation of mottle-leaf can be safely accepted, it is 

 necessary to show that the disease can be produced experimentally, and 

 that too under conditions admitting of scientific analysis. Additional 

 studies already projected may throw further light on this subject. 



Whatever may ultimately be found to be the primary cause of mottle- 

 leaf, the preceding investigations strongly suggest that the leaves are 

 not suffering from inadequate supplies of potassium, phosphorus, or 

 nitrogen. We have also found little, if any, indication of a deficiency of 

 iron. 



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